1. Field of the Invention
This invention relates to a crank angle sensor for an internal combustion engine and a cylinder identification system utilizing the same, more particularly to such a sensor and a system which enable cylinder identification to be conducted in a simple manner in a multicylinder internal combustion engine.
2. Description of the Prior Art
As the minimum information required for electronically controlling fuel injection, ignition timing and the like in a multi-cylinder internal combustion engine it is necessary to have at least cylinder identification information and reference piston position information for the respective cylinders. The traditional way of obtaining this information has been to use two rotors (pulsers), provide one rotor with a single marker (projection, slit etc.), provide the other rotor with a number of markers equal to the number of cylinders at positions corresponding to the reference piston positions of the respective cylinders, accommodate the rotors in a distributor, for example, and rotate them synchronously with the rotation of the engine, and obtain the information by detection using two electromagnetic conversion means or optical detection means fixed opposite the rotors.
Since this method required two rotors, there was developed a method using a single rotor having two types of markers (slits), one for cylinder identification and the other for reference position detection, and carrying out the detection with two optical detection means. In addition, Japanese Laid-open Patent Publication No. Hei 3(1991)-121,237 teaches an improvement on this method in which the number of cylinder identification markers is increased to two so as to enable cylinder identification in a half turn of the rotor. More specifically, in the method disclosed in this laid-open patent publication a number of reference position markers equal to the number of cylinders are provided on the outer periphery of the rotor, two cylinder identification markers are provided on the inner periphery of the rotor as offset in phase by 180.degree., the logic state of the values detected by two pairs of optical detection means disposed opposite the rotor is stored in memory beforehand for each reference position and the cylinder with which each reference position is associated is identified from the stored logic states.
However, these earlier proposed techniques lead to structurally complicated devices since they require provision of two types of markers in the radial direction of the rotor. They also limit where the device can be installed since installation is not possible at a place where a large space cannot be secured in the radial direction of the rotor.